Disposable lids for containers such as beverage cups, food cups, and the like, are well known. Usually, when such lids are disposable, they are made from an inexpensive thin, flexible plastic material, such as polystyrene; which, however does not have a significant amount of elasticity. Therefore, in order to be able to be placed over and removed from the bead of a container, the lids must be designed in such a manner that they have a so-called "garter-spring" configuration. This configuration comprises a plurality of convolutions or corrugations, or other protruberances, formed on the skirt portion of the lid.
By so configuring cup lids and lids for food cups and the like, such lids may be applied to and removed from the container at least once, after which they are usually disposed of. However, the lids must also first be stripped from the mould on or in which they are made.
Certain difficulties have arisen from previous designs, including difficulties in stripping the lids from moulds, causing deformations or stress failure in the material of the lids, or requiring special stripping stations which add to the expense of lid production and which may slow down the process of production.
Moreover, even though a lid may be designed to fit a cup having a particular dimension, the manufacturing tolerances by which such cups or other containers may be produced are such that the diameter of the rim or mouth of the container, or the size of the bead formed at the outer edge of the container, may vary significantly, so that lids designed to fit such containers having a nominal size may not, in fact, do so. This may result in a container which is much inclined to leakage around the lid, and very often results in an inadvertent stripping or dislodging of the lid from the container mouth, particularly when more than one container, each having its own lid, may be placed in a bag or other receptacle for carrying.
Still further, the space taken for shipping and storage of priior art lids has sometimes been quite significant. For example, food vendors or the like may sometimes find that the designated space that they have for lid storage, in which they expect to store a specific number of lids as received from the manufacturer, may not be quite enough space; or as a corollary, either the producer of the lids or the food vendor may wish to store more lids in a given amount of space. The present invention provides a lower stacking height, so that each lid occupies a somewhat smaller volume, which may be significant when storage of lids in amounts of thousands or even millions or such lids is considered.
Certain prior patents are particularly indicative of the kinds of lids in respect of which the present invention provides an improvement; particularly as to ease of stripability from moulds, lessening of the likelihood of inadvertent removal from a container when placed thereon, and accommodation of a wider tolerance of container sizes of a nominal size.
Included among the prior art patents of interest is Aldington, U.S. Pat. No. 2,922,563, issued Jan. 26, 1960. That patent is specifically concerned with the provision of a container closure which has a downwardly and outwardly flared skirt which is then corrugated, and above and inwardly of the skirt there is located a cavity for fitting to the bead of a container. Aldington is also concerned with stackability, by which lateral shifting of stacked lids relative to each other is precluded. However, lids of the sort taught in Aldington are formed in female dies or moulds, and may be easily dislodged from a container on which they are placed if they are jostled against other such lids on containers.
Negoro, U.S. Pat. No. 3,065,875, issued Nov. 27, 1962, teaches a snap-on plastic cup lid having a garter-spring flexibility in the skirt portion to permit fitting to a cup bead, but which only accommodates and fits to the cup bead discontinuously around the circumference thereof by virtue of projections formed in the skirt portion.
Yet another approach is taken by Brewer, U.S. Pat. No. 3,583,596, issued June 8, 1971--reissued as U.S. Pat. No. Re. 28,797, on May 4, 1976, with the same disclosure. Brewer provides a lid having a conical skirt in which is formed a plurality of spaced flutes, which vary in dimension from top to bottom, and which provide telescopic rigidity to the skirt with sufficient conical strength to adapt to the bead of the cup. Brewer is particularly concerned with nesting and stacking, and provides three spaced stacking lugs in the central panel for that purpose.
A different approach, particularly to mounting the plastic container closure on the container, is taken by Blanchard, U.S. Pat. No. 4,026,459, issued May 31, 1977. Blanchard provides a series of protruberances around the outside wall of the container, which thereby provides a discontinuous bead to grip the rim of the cup or container. Each of the protruberances may be disengaged from the rim of the container, without causing displacement of adjacent protruberances from engagement with the rim.
None of the above, nor any other known flexible plastic lid for containers for food or beverages, whether hot or cold, provides a lid which has a generally central panel and a circumferentially extending cavity which opens downwardly and inwardly to receive the bead of the container to which the lid is to be fitted, where the skirt portion which extends downwardly from the cavity has a plurality of outwardly extending projections, each of which has a substantially vertical face and substantially vertical side edges and side walls which extend inwardly from each face of each projection, and where the portions of the skirt between the outwardly extending projections, extend inwardly to form a discontinued waist which has an undercut defining the cavity in the waist portions. Each of the outwardly extending projections, and each of the discontinued waist portions between them, all terminate at their lower portions in a downwardly and outwardly sloped lower band portion. The lower band portion may, in turn, terminate at a substantially vertically disposed downwardly extending wall portion, which may generally have an outwardly turned lip at its bottom. All of the outwardly extending projections terminate at a respective upper discontinued band portion which extends inwardly and upwardly from the upper edge of each of the vertical faces of the projections, each of which terminates at the cavity at an upper undercut which is higher and less inwardly extending than the undercut of the waist portions, but which also defines the cavity.
Thus, the present invention provides a thermoformed, thin plastic lid for containers, generally formed of a plastic which has no significant amount of inherent elasticity, and which has a continuous cavity formed at its upper periphery in such a manner that the cavity can accommodate the beads of different sized containers which have a given nominal size; i.e., the bead-receiving cavity of lids of the present invention may accommodate a wide tolerance of bead size and mouth diameter of containers for which any such lid is nominally intended to be used as a closure therefor.
Moreover, the present invention provides lids of the sort spoken of above, which have a lower stacking height than prior art lids, thereby permitting more lids to be stored in the same space.
Still further, the present invention provides lids which may be formed on male moulds, a process which is somewhat less expensive and more positive as to the interior dimensions of the lid--which are the dimensions intended to be fitted to the rim or mouth of a container--and yet the lids of the present invention are easily stripped from the moulds on which they are made.
Still further, the present invention provides lids which are less likely to be disengaged from the container on which they are fitted by jostling against similar lids on similar containers.